Moxidectin

Macrocyclic lactone Avermectin/milbemycin

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2.5-6 mcg/kg (heartworm prevention) monthly; 0.2-0.4 mg/kg for mange (off-label) Monthly for heartworm prevention; daily or weekly for mange Duration: Heartworm prevention: year-round; Mange: 2-6 months
Notes: For heartworm prevention, use approved products (e.g., ProHeart). For mange, higher doses may be used under veterinary supervision.
Cat PO 2.5-6 mcg/kg (heartworm prevention) monthly; 0.2-0.4 mg/kg for mange (off-label) Monthly for heartworm prevention; daily or weekly for mange Duration: Heartworm prevention: year-round; Mange: 2-6 months
Notes: Use approved feline products. For ear mites, topical application may be used.
Horse PO 0.4 mg/kg Single dose Duration: Single administration
Notes: Administer as oral gel or paste. Repeat in 8-12 weeks for strongyle control.
Cattle SC 0.2 mg/kg Single dose Duration: Single administration
Notes: For pour-on, dose is 0.5 mg/kg topically. Withdrawal times must be observed.
Sheep PO 0.2 mg/kg Single dose Duration: Single administration
Notes: Use only in sheep with approved product. Observe withdrawal times.
Rabbit Topical 0.5 mg/kg (spot-on) Single dose, repeat in 10-14 days Duration: 2-3 treatments
Notes: Off-label use; use with caution.

Clinical Indications & Species Uses

General Indications
  • Broad-spectrum antiparasitic for nematodes and arthropods
Dog (Canine)
  • Treatment and control of gastrointestinal roundworms (e.g., Toxocara canis, Toxascaris leonina, Ancylostoma caninum, Uncinaria stenocephala)
  • Heartworm prevention (Dirofilaria immitis)
  • Treatment of sarcoptic mange
  • Treatment of demodectic mange (off-label)
  • Treatment of ear mites (Otodectes cynotis)
Cat (Feline)
  • Treatment and control of gastrointestinal roundworms (e.g., Toxocara cati, Ancylostoma tubaeforme)
  • Heartworm prevention
  • Treatment of ear mites
  • Treatment of sarcoptic mange (off-label)
Horse (Equine)
  • Treatment and control of small strongyles (cyathostomes)
  • Large strongyles (Strongylus vulgaris, S. edentatus)
  • Roundworms (Parascaris equorum)
  • Pinworms (Oxyuris equi)
  • Lungworms (Dictyocaulus arnfieldi)
  • Neck threadworms (Onchocerca spp.)
  • Habronema spp.
Cattle (Bovine)
  • Treatment and control of gastrointestinal roundworms (e.g., Ostertagia, Cooperia, Haemonchus, Trichostrongylus)
  • Lungworms (Dictyocaulus viviparus)
  • Cattle grubs (Hypoderma spp.)
  • Mange mites (Sarcoptes, Psoroptes)
  • Horn flies (Haematobia irritans)
Small Ruminants (Sheep / Goat)
  • Treatment and control of gastrointestinal roundworms (e.g., Haemonchus contortus, Teladorsagia, Trichostrongylus)
  • Lungworms (Dictyocaulus filaria)
  • Nasal bots (Oestrus ovis)
Rabbit & Small Mammals
  • Treatment of ear mites (Psoroptes cuniculi)
  • Treatment of gastrointestinal nematodes (off-label)
Exotic & Other Species
  • Treatment of ear mites in ferrets
  • Treatment of mites in guinea pigs (off-label)
  • Treatment of nematodes in reptiles (off-label)

Pharmacology & Mechanism of Action

Drug Class: Macrocyclic lactone | Pharmacological Group: Avermectin/milbemycin

Mechanism of Action: Moxidectin is a macrocyclic lactone that binds selectively to glutamate-gated chloride channels in nerve and muscle cells of invertebrates. This binding increases cell membrane permeability to chloride ions, causing hyperpolarization and flaccid paralysis of the parasite. It also interacts with gamma-aminobutyric acid (GABA) receptors in some parasites, but the primary action is on glutamate-gated channels. Mammals have these channels only in the central nervous system, and moxidectin does not readily cross the blood-brain barrier, making it relatively safe in mammals at therapeutic doses.

Pharmacodynamics: Moxidectin has broad-spectrum activity against nematodes, arthropods, and some ectoparasites. It is effective against both adult and larval stages of many gastrointestinal roundworms, lungworms, and certain external parasites. Its potency is generally higher than ivermectin against some parasites, and it has a longer duration of action due to its lipophilic nature and accumulation in fat tissue. It also has activity against some microfilariae and inhibits larval development.

⚡ Pharmacokinetics Summary

Absorption: Moxidectin is well absorbed after oral administration in most species, with peak plasma concentrations occurring within 4-8 hours in dogs and cats. In ruminants, oral absorption is lower due to rumen degradation, but it is still effective. Subcutaneous and topical formulations provide sustained absorption.
Distribution: Moxidectin is highly lipophilic and distributes widely into tissues, especially adipose tissue, from which it is slowly released. It has a large volume of distribution. It crosses the blood-brain barrier to a limited extent in mammals, but is generally safe. It is excreted in milk and crosses the placenta.
Metabolism: Moxidectin is metabolized primarily in the liver via cytochrome P450 enzymes, with hydroxylation and demethylation being major pathways. Metabolites are less active than the parent compound.
Excretion: Moxidectin is excreted primarily in feces via bile, with a small amount excreted in urine. In lactating animals, a significant amount is excreted in milk. The elimination half-life is long, especially in dogs (up to 2-3 weeks) and cattle (up to 2 weeks).
Half-Life: Dogs: ~14-28 days; Cats: ~14 days; Cattle: ~14 days; Horses: ~8-10 days
Bioavailability: Oral bioavailability: Dogs ~80%, Cats ~70%, Cattle ~30-40% (due to rumen degradation), Horses ~50%. Subcutaneous and topical formulations have high bioavailability.
Protein Binding: Moxidectin is highly protein-bound (>90%) in plasma.

Available Formulations & Strengths

Oral Tablet 30 mcg, 68 mcg, 136 mcg (for dogs) (PO)
Oral Liquid 0.1% (for dogs and cats) (PO)
Injectable Solution 1% (10 mg/mL) for cattle (SC)
Pour-on Solution 0.5% (5 mg/mL) for cattle (Topical)
Oral Gel 1% (10 mg/g) for horses (PO)
Spot-on Solution 1% (10 mg/mL) for cats and dogs (Topical)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to moxidectin or other macrocyclic lactones
  • Do not use in dogs with severe debilitation or malnutrition
  • Do not use in puppies under 6 weeks of age (for some products)
  • Do not use in cats under 6 weeks of age (for some products)
  • Do not use in cattle producing milk for human consumption (unless specifically approved)
  • Do not use in horses intended for human consumption (in some countries)
  • Do not use in animals with known liver disease (caution)
Warnings & Clinical Precautions:
  • Use with caution in dogs with collie or other herding breeds that may have MDR1 gene mutation (ivermectin sensitivity) – moxidectin is generally safer but still use caution.
  • Do not administer intravenously or intramuscularly to any species.
  • Avoid use in sick or stressed animals.
  • In cattle, do not use within 28 days of slaughter (withdrawal time varies by formulation).
  • In lactating dairy cattle, do not use in animals producing milk for human consumption (unless approved).
  • Keep out of reach of children.
  • Do not contaminate water sources.
  • Use with caution in animals with compromised blood-brain barrier (e.g., meningitis).
  • For topical formulations, avoid contact with eyes and mucous membranes.

Adverse Effects & Reactions

Common:

  • Salivation (especially in cats after oral administration)
  • Vomiting (rare in dogs)
  • Lethargy
  • Local injection site reactions (swelling, pain)

Serious / Severe:

  • Neurological signs (ataxia, tremors, seizures) especially in sensitive breeds or overdose
  • Depression
  • Coma
  • Death (rare)

Rare:

  • Allergic reactions (urticaria, angioedema)
  • Hepatotoxicity
  • Bone marrow suppression (with prolonged high doses)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
P-glycoprotein inhibitors (e.g., ketoconazole, itraconazole, cyclosporine) May increase moxidectin concentrations and risk of toxicity. High
Other macrocyclic lactones (e.g., ivermectin) Additive effects and increased risk of toxicity. Moderate
GABAergic drugs (e.g., barbiturates, benzodiazepines) Potential additive CNS depression. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Ataxia
  • Tremors
  • Mydriasis
  • Depression
  • Salivation
  • Vomiting
  • Seizures
  • Coma
  • Respiratory failure

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent oral ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide IV fluids, respiratory support, and anticonvulsants (e.g., diazepam) if seizures occur. Monitor vital signs and neurological status. In severe cases, provide intensive care.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 0 days

Withdrawal times vary by formulation and country. For cattle injectable, meat withdrawal is 28 days; for pour-on, 28 days. For sheep, meat withdrawal is 14 days. Not approved for use in lactating dairy cattle or in poultry. Always follow label and local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs, cats, cattle, and horses in the US. Some formulations are approved for sheep in other countries.

Extra-Label (Off-Label) Use: In the US, moxidectin is available by prescription. Extra-label use in food animals requires a valid veterinary-client-patient relationship and observance of extended withdrawal times. In the EU, similar regulations apply. Use in non-food animals is generally allowed under veterinary supervision.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Moxidectin is a broad-spectrum antiparasitic with a long duration of action. It is particularly useful for heartworm prevention in dogs and cats, and for control of gastrointestinal parasites in livestock. In horses, it is effective against small strongyles and is often used in rotation with other dewormers to reduce resistance. In cattle, it provides persistent activity against many nematodes. Due to its lipophilicity, it accumulates in fat and is slowly released, providing prolonged activity. However, this also means it has a long withdrawal time in food animals. Moxidectin is generally well tolerated, but caution is advised in breeds with MDR1 mutations. Always use according to label directions and under veterinary guidance.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)